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SUS301-EH is widely used as a material for exhaust system gaskets, however, at temperatures in excess of 400°C, it can not be used as gas-seal ability of the material declines due to its reduced hardness. The following methods were found to be effective in controlling the softening of stainless steel at high temperatures: (1) The addition of a nitrogen component; (2) Stabilization of the austenite structure; (3) The addition of a molybdenum component. The addition of 0.5% nitrogen to austenitic stainless steel containing molybdenum has enabled the speed of softening at high temperatures to be significantly reduced, due to strain aging by solid nitrogen below 600°C and the combined effects of precipitation hardening and control of growth of recrystallized grains through the precipitation of fine Cr2N on the dislocations and the grain boundary above 600°C.

As trends of automobile engine exhaust gas temperature are reducing emissions, the material for the exhaust components have been changed from ductile irons to ferritic cast alloys or stainless steel, further to austenitic cast alloys for higher performance engines. The current austenitic alloys, however, have thermal fatigue failure over 1273K. The authors developed excellent thermal fatigue resistant austenitic cast alloys, by investigating the effects of alloying elements on strength and thermal expansion, which correlate with thermal fatigue property. Developed alloys are expected to apply to exhaust components at gas temperatures over 1273K.